1. Field of the Invention
This invention relates to a marking device used in marking the surfaces of products during molding process, more specifically, it relates to a marking device having a high operability as well as capability of preventing molten material penetration during high-temperature molding process.
2. Description of the Background Art
Today, various kinds of resin materials or metallic materials are used for molding process thanks to the development of technologies for molding as well as resin development. Those materials sometimes have a relatively high melting point and require a high temperature for a molding process such as aluminum die cast molding.
Many molding factories manufacturing put an identification label such as manufacturing date or manufacturing line number on their products. Japanese Patent Publication No. 2008-68506 discloses various kinds of marking devices for labeling such identification information. One of the various marking devices is shown in FIG. 19 disclosed in Japanese Patent Publication No. 2008-68506. FIG. 19(a) is a plain view of the marking device and FIG. 19(b) is a cross sectional view of the marking device. FIG. 19(c) is a bottom view of the marking device.
The marking device (M) in FIG. 19 comprises an outer shell (O) in a cylindrical shape, a rotatable tube (R) in a cylindrical shape received in the outer shell (O), an indicator (I) inserted in the rotatable tube (R), a seat member (S) supporting the rotatable tube (R) and indicator (I) within the outer shell (O), and a lid (L) closing a bottom surface of the outer shell (O).
The marking device (M) is fixed to an attachment hole of a molding device. Upper surfaces of the outer shell (o), the rotatable tube (R) and the indicator (I) appears in a cavity of the molding device. Each of the top surfaces of the outer shell (O), rotatable tube (R) and indicator (I) has carved marks (C). When the molten material injected into the cavity flows into the carved marks, identification relief on a surface of the mold product appears after solidification of the molten material. In general, the top surfaces of the outer shell (O), rotatable tube (R) and indicator (I) are leveled with each other to form a flat top surface of the marking device (M) so that their borders do not create annular lines or steps on the mold product.
A marking device (M) disclosed in Japanese Patent Publication No. 2008-68506 internally includes a control mechanism which allows to select a motion of the rotatable tube (R), rotation or stationariness, depending on a rotation direction of the indicator (I). For example, when the indicator (I) is rotated in a clockwise direction, the rotatable tube (R) remains still, on the other hand, when the indicator (I) is rotated in an opposite direction, then the rotatable tube (R) rotates in the same direction as the indicator (I) rotates. Thus, the marking device (M) disclosed in Japanese Patent Publication No. 2008-68506 has a high operability, however, it will be lost when used in a high-temperature molding process such as aluminum die cast molding.
Generally, a kinetic viscosity of a fluid decreases according to an increase in temperature. This means that a molten material with a low kinetic viscosity may enter into a small gap. For example, when the marking device (M) disclosed in Japanese Patent Publication No. 2008-68506 is used for aluminium diecast molding, a molten aluminium with a low kinetic viscosity flows into the border between the outer shell (O) and the rotatable tube (R), and between the indicator (I) and the rotatable tube (R). The flowing molten aluminium is subjected to a cooling process for solidification after a molten aluminium injection process. The solidified aluminium between the outer shell (O) and the rotatable tube (R), and between the indicator (I) and the rotatable tube (R) may prevent the rotation of the indicator (I) and rotatable tube (R).
Japanese Utility Model Publication S61-44810 discloses a marking device (M1) with an effective structure preventing the flow of the molten material. FIG. 20 is a schematic perspective view of Japanese Utility Model Publication S61-44810.
The marking device (M1) disclosed in Japanese Utility Model Publication S61-44810 comprises head (H) in a frusto-conical shape and a leg (E) protruding downwardly from the bottom of the head (H), and the marking device is inserted into a tapered hole (T) formed on a molding device (D). The marking device (M1) is fixed to the molding device (D) by engaging with nut provided with the bottom surface of the molding device (D) and a threaded portion of the leg (E).
A periphery surface of the head (H) contacts to that of the tapered hole (T). Engagement between the nut and the leg (E) causes a high pressure therebetween. Thus, it is possible to prevent a penetration of the molten material into a border between the head (H) and tapered hole (T).